In the information society of these days, electronic display devices are more important as information transmission media and various electronic display devices are widely applied for industrial apparatus or home appliances. Such electronic display devices are being continuously improved to have new appropriate functions for various demands of the information society.
In general, electronic display devices display and transmit various pieces of information to users who utilize such information. That is, the electronic display devices convert electric information signals outputted from electronic apparatus into light information signals recognized by users through their eyes.
In the electronic display devices dividing into an emissive display device and a non-emissive display device, the emissive display device displays light information signals through a light emission phenomena thereof and the non-emissive display device displays the light information signals through a reflection, a scattering or an interference thereof. The emissive display device includes a cathode ray tube (CRT), a plasma display panel (PDP), a light emitting diode (LED) and an electroluminescent display (ELD). The emissive display device is called as an active display device. Also, the non-emissive display device, called as a passive display device, includes a liquid crystal display (LCD), an electrochemical display (ECD) and an electrophoretic image display (EPID).
The CRT has been used for a television receiver or a monitor of a computer as the display device for a long time since it has a high quality and a low manufacturing cost. The CRT, however, has some disadvantages such as a heavy weight, a large volume and a high power dissipation.
Recently, the demand for a new electronic display device is greatly increased such as a flat panel display device having excellent characteristics, for example, thin thickness, light weight, low driving voltage and low power consumption. Such flat panel display devices can be manufactured according to the rapidly improved semiconductor technology.
In the flat panel devices, a liquid crystal display (LCD) device has been widely utilized for various electronic devices because the LCD device has thin thickness, low power dissipation and high display quality approximately identical to those of the CRT. Also, the LCD device can be operated under a low driving voltage and can be easily manufactured so that the LCD device is widely used for various electronic apparatuses.
The LCD devices are generally divided into a transmission type LCD device, a reflection type LCD device, and a reflection-transmission type LCD device. The transmission type LCD device displays information by using an external light source and the reflection type LCD device displays information by using a natural light. The reflection-transmission type LCD device operates in a transmission mode for displaying an image using a built-in light source of the LCD device in a room or in a dark place where an external light source does not exist, and operates in a reflection mode for displaying the image by reflecting an incident light in the outside.
The reflection type liquid crystal display device, however, shows relatively dark images and cannot sufficiently apply to display fine pitches or color images, so the reflection type liquid crystal display device has been utilized to only display simple figures or letters. Hence, the reflection type liquid crystal display device should have fine pitches and a high reflectivity as well as display color images in order to be used for various electronic display devices. In addition, the reflection type liquid crystal display device has a sufficient brightness, a rapid response speed, and an improved image contrast.
In the recent reflection type liquid crystal display device, the brightness of the reflection type liquid crystal display device has been improved by means of combining the increase of the reflectivity of the reflection electrode with the super aperture ratio technology. A reflection electrode having numerous fine convexes and concaves is disclosed in U.S. Pat. No. 5,610,741 issued to Naofumi Kimura, entitled “REFLECTION TYPE LIQUID CRYSTAL DISPLAY DEVICE WITH BUMPS ON THE REFLECTOR”.
Meanwhile, the present inventors have been developed a reflection electrode causing a uniform diffused reflection to improve the quality of an image and filed this invention in Korean Intellectual Property Office (KIPO) on Mar. 4th, 1999. Such reflection electrode is disclosed in Korean Ser. No. 1999-7093, entitled “A REFLECTION TYPE LIQUID CRYSTAL DISPLAY DEVICE AND A METHOD FOR MANUFACTURING THE SAME” which is now pending in KIPO and is subject to the applicant of this application.
FIG. 1 is a plane view showing a reflection electrode or patterns on a photo mask for forming the reflection electrode according to the above-mentioned application.
Referring to FIG. 1, the reflection electrode includes a first region 14 and second region 16, which have relatively high and low heights in a pixel area. The second region 16 is enclosed with the first region 14 such as closed curves. The first region 14 is formed to have a constant width. The first region 14 has a groove shape having a height relatively lower than the second region 16. The second region 16 has a protuberance shape having a height relatively higher than the first regions 14, so the second region 16 functions as a micro lens.
To form a plurality of micro lenses on the reflection electrode, an organic insulating layer is formed on a first insulating substrate having thin film transistors and then, should be exposed and developed using a photo mask having the patterns shown in FIG. 1.
FIGS. 2A and 2B are cross-sectional views taken along lines of A1-A1′ and B1-B1′ in FIG. 1, which illustrate a method of forming a plurality of grooves on the organic insulation layer.
Referring to FIGS. 2A and 2B, a photo mask 20 having patterns corresponding to grooves for forming micro lenses is located over an organic insulation layer 12 in order to form a plurality of first regions 14 having the groove shape thereon. In this case, the photo mask 20 has the patterns identical to the shape of the reflection electrode shown in FIG. 1. Specifically, mask patterns corresponding to the first regions 14 are formed on a transparent substrate, thereby forming the photo mask 20 as shown in FIG. 1. After the organic insulation layer 12 is exposed and developed using the photo mask 20, a plurality of grooves 14 (that is, the first regions 14) are formed in the surface of the organic insulation layer 12.
Each of the first regions 14 is formed such that a width Wa in a first direction (that is, the line of A1-A1′ in FIG. 1) is identical to a width Wb in a second direction (that is, the line of B1-B1′ in FIG. 1). Since the first regions 14 are formed to have uniform widths Wa and Wb, a reflective efficiency is increased to thereby improve an image quality of the reflection type liquid crystal display device.
The above-mentioned reflection electrode has constant reflectivity concerning all directions including the horizontal and vertical directions because the micro lenses of the reflection electrode (that is, the second regions 16) are isotropically formed in all directions. The reflection electrode, however, cannot be applied to an electronic device demanded to have high reflectivity in a certain direction such as a cellular phone. In case that the entire patterns may be varied in order to increase the reflectivity of the reflection electrode in a specific direction, processing conditions should be optimized once more and other problem such as a symmetry concerning the entire substrates may occur.